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2018 WAEC Mathematics Theory (a) Copy and complete the table of values for y = 2x\(^{2}\) + x -...

Mathematics
WAEC 2018

(a) Copy and complete the table of values for y = 2x\(^{2}\) + x - 10 for -5 \(\leq\) x \(\leq\) 4.

x -5 -4 -3 -2 -1 0 1 2 3 4
y     5   -9 -10   0    

(b) Using scales of 2cm to 1 unit on the x- axis and 2cm to 5 units on the y- axis, Draw the graph of y = 2x\(^{2}\) + x - 10 for -5 \(\leq\) x \(\leq\) 4.

(c) Use the graph to find the solution of :

(i) 2x\(^{2}\) + x = 10

(ii) 2x\(^{2}\) + x - 10 = 2x

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Explanation

(a) 

x -5 -4 -3 -2 -1 0 1 2 3 4
y 35 18 5 -4 -9 -10 -7 0 11 26

 

(b) 

(c)(i) 2x\(^{2}\) + x = 10 \(\equiv\) 2x\(^{2}\) + x - 10 = 0

Thus, the solution of 2x\(^{2}\) + x - 10 = 0 are the values of x at which the curve cuts the x- axis.

    x = -2.5 or x = 2.

(ii)  2x\(^{2}\) + x - 10 = 2x

To solve the given equation, we first draw the graph of y = 2x: when x =  -2, y = 2(-2) = -4; when x = 3, y = 2(3) = 6.

The values of x at which y = 2x\(^{2}\) + x - 10 and y = 2x intersect give the solution of 2x\(^{2}\) + x - 10 = 2x.

These are x = -2 or x = 2.5.


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